This invention relates to the preparation of halogen substituted hydrocarbons and more particularly to the use of equilibrium reactions for preparing halogen substituted hydrocarbons containing fluorine.
There has been considerable recent interest in halogen substituted ethanes containing fluorine and hydrogen. Many of these materials can be used not only as blowing agents and refrigerants, but also as starting materials for preparing other useful compounds.
U.S. Pat. No. 4,766,260 discloses an improved gas-phase process for the manufacture of 1,1,1-trifluorodichloroethane (i.e., HCFC-123) and 1,1,1,2-tetrafluorochloroethane (i.e., HCFC-124) by contacting a suitable tetrahaloethylene with hydrogen fluoride in the presence of a selected metal on a high fluorine content alumina support, the reaction being conducted under controlled conditions whereby the production of pentafluoroethane (i.e., HFC-125) is minimized. U.S. Pat. No. 4,766,260 discloses that intermediates formed during the course of the invention, such as CHF2CClF2, CHClFCClF2, CHCl2CClF2, CClFxe2x95x90CCl2 and CHCl2CCl2F can be recycled to the reactor for the production of additional 1,1,1-trifluorodichloroethane and 1,1,1,2-tetrafluorochloroethane; and that 1,1,1-trifluorodichloroethane can be recycled to the reactor for the production of additional 1,1,1,2-tetrafluorochloroethane when this is desired. It is often desirable to avoid the use and production of unsaturated materials, and there is thus a need for additional techniques which selectively yield saturated halogen substituted hydrocarbons containing fluorine and hydrogen such as HCFC-123, HCFC-124 and HFC-125.
Chromium-containing catalysts have been used in conjunction with disproportionations and other reactions involving halogen-substituted ethanes. For example, U.S. Pat. No. 4,145,368 discloses a process for manufacturing 1,1,1-trifluoro-2,2-dichloroethane by reaction of 1,1,1-trifluoro-2,2,2-trichloroethane with 1,1,1-trifluoro-2-chloroethane over a solid catalyst such as Cr2O3. The use of catalysts containing chromium in a valence state of three to six and either oxide alone or oxide and fluoride is disclosed. U.S. Pat. No. 3,787,331 discloses use of a chromium-containing catalyst in disproportionating and isomerizing CF2Clxe2x80x94CFCl2; and U.S. Pat. No. 3,651,156 exemplifies the disproportionation reaction of C2F3Cl3 passed over a catalyst obtained by fluorination of chromium hydroxide.
U.S. Pat. No. 4,605,798 discloses a process for the preparation of trichlorotrifluoroethanes, dichlorotetrafluoroethanes, and monochloropentafluoroethane utilizing three reactors, one of which is used for a fluorination-dismutation reaction. The catalysts used in these reactors comprise supported or non-supported oxides or halides of chromium among others.
We have found that catalysts selected from the group of catalysts consisting of catalysts containing chromium in a valence state of three to six as an oxide, a halide, or as halided oxide and supported catalysts containing at least one metal selected from cobalt, copper, iron, manganese, nickel and zinc are effective in equilibrating CF3CFHCl with its disproportionation products CF3CHCl2 and CF3CF2H; and that the equilibration constant for the disproportionation varies with temperature over the range of 50xc2x0 C. to 500xc2x0 C., with the formation of CF3CFHCl becoming more favored as the temperature increases.
The present invention involves at least partial equilibration of the halohydrocarbon CF3CFHCl (HCFC-124) with halohydrocarbons CF3CHCl2 (HCFC-123) and CF3CF2H (HFC-125) using a vapor phase reaction. In this equilibration the halogens on the carbon containing the hydrogen exchange. All the compounds involved in the interconversion contain exactly two carbons and one hydrogen.
A method is provided in accordance with this invention for increasing in a composition the mole fraction of a selected compound of the formula CF3CHFxCl2xe2x88x92x where x is an integer from 0 to 2 relative to the total mole fraction of the other two compounds having said formula which comprises the steps of: (a) providing a gaseous composition comprising at least one compound of said formula provided that (i) if the selected compound is either CF3CHCl2 or CF3CHF2, said gaseous composition comprises CF3CHFCl and the mole fraction of the selected compound relative to the other two compounds in said gaseous composition is less than its equilibrium amount at 50xc2x0 C., and (ii) if the selected compound is CF3CHFCl, said gaseous composition comprises CF3CHCl2 and CF3CHF2 and the mole fraction of the selected compound relative to the other two compounds in said gaseous composition is less than its equilibrium amount at 500xc2x0 C.; (b) contacting said gaseous composition with a catalyst selected from the group of catalysts consisting of catalysts comprising chromium as an oxide, as a halide or as a halided oxide, in a valence state of three to six, and supported catalysts containing at least one metal selected from cobalt, copper, iron, manganese, nickel and zinc, for a time sufficient to provide substantial interconversion among the three compounds having said formula; and (c) providing during said catalyst contact a temperature within the range of about 50xc2x0 C. to 500xc2x0 C. at which the mole fraction of the selected compound relative to the other two compounds increases.
The method, preferably supplemented by the steps of separating at least a portion of the selected compound from the interconverted composition of step (c); and contacting at least a portion of the compounds remaining after said separation with a catalyst selected from said group of catalysts at a temperature within the range of about 50xc2x0 C. to 500xc2x0 C. and for a time sufficient to produce an additional quantity of said selected compound by providing substantial interconversion; can be advantageously included in a process for preparing halogen substituted ethanes to increase the yield of the selected compound relative to the total yield of the other two compounds having the above-referenced formula.
The invention deals with processes employing the interconversion of CF3CFHCl (HCFC-124) with CF3CHCl2 (HCFC-123) and CF3CF2H(HFC-125) using selected catalysts. The preferred catalysts of this invention comprise chromium in a valence state of three to six as an oxide (e.g., Cr2O3), as a halide (e.g., CrX3 where each X is selected from chlorine and fluorine) or as a halided oxide (e.g., Cr2O3 treated with CCl3F or CCl4). The chromium catalysts of this invention can be supported or unsupported. Other catalysts which may be used for the interconversion of this invention include supported catalysts containing at least one metal selected from cobalt, copper, iron, manganese, nickel and zinc.
A method is provided in accordance with this invention for increasing in a composition the mole fraction of a selected compound of the formula CF3CHFxCl2xe2x88x92x where x is an integer from 0 to 2 relative to the total mole fraction of the other two compounds having said formula comprising the steps of: (a) providing a gaseous composition comprising at least one compound of said formula provided that (i) if the selected compound is either CF3CHCl2 or CF3CHF2, said gaseous composition comprises CF3CHFCl and the mole fraction of the selected compound relative to the other two compounds in said gaseous composition is less than its equilibrium amount at 50xc2x0 C., and (ii) if the selected compound is CF3CHFCl, said gaseous composition comprises both CF3CHCl2 and CF3CHF2 and the mole fraction of the selected compound relative to the other two compounds in said gaseous composition is less than its equilibrium amount at 500xc2x0 C.; (b) contacting said gaseous composition, with a catalyst selected from the group of catalysts consisting of catalysts comprising chromium as an oxide, as a halide or as a halided oxide, in a valence state of three to six, and supported catalysts containing at least one metal selected from cobalt, copper, iron, manganese, nickel and zinc, for a time sufficient to provide substantial interconversion among the three compounds having said formula; and (c) providing during said catalyst contact a temperature within the range of about 50xc2x0 C. to 500xc2x0 C. at which the mole fraction of the selected compound relative to the other two compounds increases.
Suitable compositions comprising the compounds of the formula CF3CHFxCl2xe2x88x92x may be provided as a product (e.g., a reaction product) containing all three compounds. Alternatively either HCFC-124, or both HCFC-123 and HFC-125 may be provided. It will be evident that even where HCFC-124 is initially provided without HCFC-123 and/or HFC-125 or where both HCFC-123 and HFC-125 are initially provided without HCFC-124, even partial equilibration will produce a quantity of the compound(s) not initially provided. Accordingly, gaseous mixtures comprising all three compounds of the formula CF3CHFxCl2xe2x88x92x may be provided in accordance with step (a), and interconversion (i.e., disproportionation or conproportionation) among HCFC-124, HCFC-123, and HFC-125 may be achieved in accordance with this invention at suitable temperatures.
The chromium catalysts of this invention can be used as a single component or combined with a support such as alumina or carbon. The catalysts of this invention which do not contain chromium (i.e., catalysts containing cobalt, copper, iron, manganese, nickel and/or zinc) should be supported. Supported catalysts (e.g., supported chromium oxides) can be prepared by impregnation of a pre-formed support, co-precipitation or co-evaporation. Such methods are well-known in the art. Reference is made to U.S. Pat. No. 4,766,260 for further discussion of supported metal catalysts.
The preferred catalysts of this invention contain chromium as an oxide, as a halide, or as a halided oxide. By halided chromium oxide is meant a material comprising chromium, oxygen, and a halogen, the halogen being either chlorine or fluorine. The halogen content can vary from 1% to nearly 10% with either halogen. The remainder of the material may include chromium oxide.
Catalysts based on fluorided chromia (Cr2O3) can be prepared prior to reaction by treatment with a vaporizable fluorine-containing fluorinating compound, such as HF, CCl3F (CFC-11), CClF2 (CFC-12), or CCl2FCClF2 (CFC-113). Catalysts based on chlorided chromia can be prepared prior to reaction by treatment with a vaporizable chlorine-containing chlorinating compound, such as CCl4 or C2Cl4. The surface halogenation takes place at elevated temperatures until the desired degree of fluorination is obtained, e.g., at about 200xc2x0 C. to about 450xc2x0 C. The treatment can conveniently be done in the reactor which is to be used for equilibration.
A suitable catalyst may be prepared, for example, as follows:
A quantity of chromia (Cr2O3) is dried until essentially all moisture is removed, e.g., for about 2 hours at 400xc2x0 C. The dried catalyst is then transferred to the reactor to be used. The temperature is then lowered to about 200xc2x0 C., and CFC-12 in N2 is passed through the reactor. The N2 can be gradually reduced until only CFC-12 is being passed through the reactor. At this point the temperature is increased to about 350xc2x0 C. and held at that temperature to convert the Cr2O3 to the desired halide content. If too much activator is used, the resulting bulk CrX3 will not be as active as surface treated oxide. If too little is used, further activation will occur when the actual process is started.
The interconversion using the catalyst of the instant invention is conducted at 50xc2x0 C. to 500xc2x0 C., preferably about 200xc2x0 C. to 400xc2x0 C. Depending upon the selected compound desired, mixtures of HCFC-124, HCFC-123 and HFC-125 in any proportion may be used as feed to the equilibration reactor. Preferably, where it is desirable to produce CF3CFHCl, the gaseous composition of step (a) is derived from a feed of CF3CHCl2 and CF3CHF2; and where it is desirable to produce CF3CHCl2 and/or CF3CHF2, the gaseous composition of step (a) is derived from a feed of CF3CFHCl.
The contact time in the vapor phase process can vary widely depending on the degree of conversion desired and generally will be about 5 to 180 seconds, preferably about 60 to 90 seconds.
The halohydrocarbon may be fed as is or diluted with an inert gas such as nitrogen, helium or argon.
The interconversion of HCFC-124 with HCFC-123 and HFC-125 may be conducted in any suitable reactor, including fixed and fluidized bed reactors. The reaction vessel should be constructed from materials which are resistant to the corrosive effects of hydrogen halides, such as Hastelloy(copyright) nickel alloy and Inconel(copyright) nickel alloy.
In accordance with this invention a method is provided for increasing the yield of a selected compound of the formula CF3CHFxCl2xe2x88x92x where x is an integer from 0 to 2 relative to the total yield of the other two compounds having said formula in a process for preparing halogen substituted ethanes containing fluorine. A preferred method includes the steps of (a) providing a gaseous composition comprising at least one compound of said formula provided that (i) if the selected compound is either CF3CHCl2 or CF3CHF2, said gaseous composition comprises CF3CHFCl and the mole fraction of the selected compound relative to the other two compounds in said gaseous composition is less than its equilibrium amount at 50xc2x0 C., and (ii) if the selected compound is CF3CHFCl, said gaseous composition comprises both CF3CHF2 and CF3CHCl2 and the mole fraction of the selected compound relative to the other two compounds in said gaseous composition is less than its equilibrium amount at 500xc2x0 C.; (b) contacting said gaseous composition with a catalyst selected from the group of catalysts consisting of catalysts comprising chromium as an oxide, as a halide or as a halided oxide, in a valence state of three to six, and supported catalysts containing at least one metal selected from cobalt, copper, iron, manganese, nickel and zinc, for a time sufficient to provide substantial interconversion among the three compounds having said formula; and (c) providing during said catalyst contact a temperature within the range of about 50xc2x0 C. to 500xc2x0 C. at which the mole fraction of the selected compound relative to the other two compounds increases; (d) separating at least a portion of the selected compound from the interconverted composition of step (c); and (e) contacting at least a portion of the compounds remaining after said separation with a catalyst selected from the group of catalysts consisting of catalysts comprising chromium as an oxide, as a halide or as a halided oxide in a valence state of three to six, and supported catalysts containing at least one metal selected from cobalt, iron, manganese, nickel, and zinc, at a temperature within the range of about 50xc2x0 C. to 500xc2x0 C. and for a time sufficient to produce an additional quantity of said selected compound by providing substantial interconversion.
Pressure is not critical. Atmospheric and superatmospheric pressures are the most convenient and are therefore preferred.
Separation of the selected compound as provided by step (d) may be accomplished by conventional methods (e.g., fractional distillation). The catalyst contact step (e) can be accomplished in a separate contact unit or can, where suitable, be accomplished by recycling of compounds remaining after separation to the catalyst contact of steps (b) and (c).
HFC-125 and HCFC-123 may be used in accordance with this invention to provide HCFC-124 which is an important reagent for producing the refrigerant CF3CH2F. This invention allows HFC-125 produced during commercial HCFC-124 production by hydrofluorination to be recycled with intermediate HCFC-123 for added HCFC-124 production. The interconversion can also produce HFC-125 from HCFC-124 without requiring equipment resistant to HF. The product fluorocarbons of this invention are useful as refrigerants.
Practice of the invention will be made further apparent from the following non-limiting examples.